From the general state of the art, valve arrangements for controlling hydraulic drives are known, in which the control openings for controlling the supply and the outflow of the hydraulic drive are mechanically or hydraulically connected with each other. However, such valve arrangements have the disadvantage that at the working connection serving as inlet, a cavitation may occur. The cavitation and a too high speed of the inlet-controlled drive has until now been avoided by a heavy throttling of the outflow of the hydraulic drive. This heavy throttling, however, results in a poor energetic efficiency. As a solution to this problem, EP 0 809 737 B1, U.S. Pat. No. 5,138,838, U.S. Pat. No. 5,568,759 and U.S. Pat. No. 5,960,695 suggest valve arrangements, with which the supply and the outflow of the hydraulic drive can be controlled separately. These solutions, however, do not meet the heavy requirements with regard to low leakage flows of the working connections, when the valves are not activated. When a load to be moved by the hydraulic drive and the speed of the drive act in the same direction, the solutions in the disclosures mentioned suggest controlling the speed by acting upon the drive with a relatively high oil pressure, which also causes a poor efficiency. U.S. Pat. No. 4,840,111 and U.S. Pat. No. 6,467,264 attempt to solve this problem in that they dispense from a high oil pressure from the supply line. However, these solution proposals require an unnecessarily high pressure in the tank pipe to avoid the cavitation when lowering the load and at the same time to require no hydraulic fluid from the pump pipe. The high pressure in the tank pipe, however, causes throttling losses, which again result in a poor energetic efficiency.
The task of the invention is to substantially improve the energy efficiency in connection with the above-described valve arrangement.